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NEW YORK (Reuters Health) - Supplements containing folic acid are known to cut levels of a protein in the blood implicated in heart disease, but a large new analysis suggests that does not translate into a lowered risk of cardiovascular disease, cancer or death.
One in every three U.S. adults reports taking multivitamins containing folic acid. The B-vitamin has long been known to help prevent anemia and to reduce the risk of birth defects such as spina bifida.
More recently, folic acid was found to have a bonus benefit: lowering levels of a protein the body makes after eating meat - homocysteine -- which has been linked to cardiovascular and other health problems.
The connection seemed to suggest that the vitamin could also be a powerful ally in the fight against heart disease, as well as stroke and cancer.
"The homocysteine hypothesis of cardiovascular disease attracted considerable interest as homocysteine is easily lowered by dietary supplementation with folic acid and other B-vitamins," lead researcher Dr. Robert Clarke of the University of Oxford, in England, told Reuters Health in an e-mail.
To see if the theory was worthy of the hype, Clarke and his colleagues collected and analyzed data from eight large trials on the subject, involving a total of 37,485 people at heightened risk for cardiovascular disease. About half of the participants were randomly assigned to take relatively high doses of folic acid -- ranging from 0.8 to 40 milligrams per day -- and the rest were given placebo pills.
A typical multivitamin in the U.S. contains around 0.4 milligrams of folic acid.
Homocysteine levels were, on average, 25 percent lower among the trial subjects taking folic acid supplements over the five or so years they were followed, compared to those on placebo.
The researchers tallied a total of 9,326 major first-time vascular events, including strokes, as well as 3,010 cases of cancer and 5,125 deaths across the studies.
However, no meaningful differences between the two groups were seen in the rates at which outcomes occurred, the researchers report in the Archives of Internal Medicine.
Of the more than 9,000 first-time vascular events in the study group, for instance, 24.9 percent were in individuals taking folic acid and 24.8 percent in those on placebo. Major coronary events were also split evenly between the vitamin group (11.4 percent) and the placebo group (11.1 percent).
"Taking folic acid supplements or adding folic acid to cereal grains in the U.S. and Canada is beneficial for prevention of neural tube defects," noted Clarke. "However, taking folic acid or other B-vitamin supplements does not cause any reduction in heart attacks, strokes, or deaths from coronary heart disease or stroke."
"The results are definitive and it is unlikely that any further trials will be set up to address this question," he added.
In a separate recent study, researchers at the UCLA Stroke Center in Los Angeles also found no reduced risk of stroke with folic acid supplementation. (See Reuters Health report, May 13, 2010.) And still another study in Norway last year linked the vitamin with a rise in cancer risk. (See Reuters Health report, November 17, 2009.)
Clarke, however, noted that his team's review found no increased risks of cancer or other conditions with folic acid intake.
"People should continue to get vitamins and minerals from a healthy balanced diet," he suggested, "unless they're advised to take supplements by their doctor or registered dietician."
SOURCE: link.reuters.com/meg28p Archives of Internal Medicine, October 11, 2010.